Close #1379 - Increment b:ale_linted when a buffer is checked

autoload/ale/engine.vim

@@ -321,6 +321,12 @@ function! ale#engine#SetResults(buffer, loclist) abort
 
         " Reset the save event marker, used for opening windows, etc.
         call setbufvar(a:buffer, 'ale_save_event_fired', 0)
+        " Set a marker showing how many times a buffer has been checked.
+        call setbufvar(
+        \   a:buffer,
+        \   'ale_linted',
+        \   getbufvar(a:buffer, 'ale_linted', 0) + 1
+        \)
 
         " Automatically remove all managed temporary files and directories
         " now that all jobs have completed.